Hi and welcome to NamePros. I don't see any value in this domain, and for your idea, I believe 3dCity.com would be much better. Of course, 3dcity is taken, but the fact remains, 3sity makes little sense.
I'm also curious about an automated service called CertifiedOfferService.com:
It is independently valued my domain name 3sity.com at over $25,000. https://www.certifiedofferservice.com/CertifiedOffer/offer/makeoffer.do?dom=3sity.com and select No for product name inclusion. That seems high but then again I tried a lot of other domain names with it that actually came out low. Thoughts?